Sequential ruthenium-catalyzed hydroamination and rhenium-catalyzed C-H bond activation leading to indene derivatives

[reaction: see text] Formal [3 + 2] annulation of arylacetylenes and alpha,beta-unsaturated carbonyl compounds is achieved in a one-pot reaction by successive treatment of the acetylenes with aniline and a catalytic amount of Ru(3)(CO)(12) and NH(4)PF(6) and C-H bond activation catalyzed by [ReBr(CO)(3)(thf)](2). The result suggests that the second rhenium-catalyzed indene formation is not disturbed by the first catalyst system.     

Rhodium-catalyzed intermolecular amidation of arenes with sulfonyl azides via chelation-assisted C-H bond activation

We report the direct amidation of arene C-H bonds using sulfonyl azides as the amino source to release N(2) as the single byproduct. The reaction is catalyzed by a cationic rhodium complex under external oxidant-free conditions in the atmospheric environment. A broad range of chelate group-containing arenes are selectively amidated with excellent functional group tolerance, thus opening a new avenue to practical intermolecular C-N bond formation.     

Cupric superoxo-mediated intermolecular C-H activation chemistry

The new cupric superoxo complex [LCu(II)(O(2)(?-))](+), which possesses particularly strong O-O and Cu-O bonding, is capable of intermolecular C-H activation of the NADH analogue 1-benzyl-1,4-dihydronicotinamide (BNAH). Kinetic studies indicated a first-order dependence on both the Cu complex and BNAH with a deuterium kinetic isotope effect (KIE) of 12.1, similar to that observed for certain copper monooxygenases.     

Towards mild metal-catalyzed C-H bond activation

Functionalizing traditionally inert carbon-hydrogen bonds represents a powerful transformation in organic synthesis, providing new entries to valuable structural motifs and improving the overall synthetic efficiency. C-H bond activation, however, often necessitates harsh reaction conditions that result in functional group incompatibilities and limited substrate scope. An understanding of the reaction mechanism and rational design of experimental conditions have led to significant improvement in both selectivity and applicability. This critical review summarizes and discusses endeavours towards the development of mild C-H activation methods and wishes to trigger more research towards this goal. In addition, we examine select examples in complex natural product synthesis to demonstrate the synthetic utility of mild C-H functionalization (84 references).     

Metal-free intermolecular oxidative C-N bond formation via tandem C-H and N-H bond functionalization

The development of a novel intermolecular oxidative amination reaction, a synthetic transformation that involves the simultaneous functionalization of both a N-H and C-H bond, is described. The process, which is mediated by an I(III) oxidant and contains no metal catalysts, provides a rapid and green method for synthesizing protected anilines from simple arenes and phthalimide. Mechanistic investigations indicate that the reaction proceeds via nucleophilic attack of the phthalimide on an aromatic radical cation, as opposed to the electrophilic aromatic amination that has been reported for other I(III) amination reactions. The application of this new reaction to the synthesis of a variety of substituted aniline derivatives is demonstrated.     

Tuning N-heterocyclic carbenes in T-shaped Pt(II) complexes for intermolecular C-H bond activation of arenes

Small change matters: T-shaped Pt(II) complexes with less flexible substituents, than, for example, isopropyl or tert-butyl groups, on N-heterocyclic carbene (NHC) ligands allow for C-H bond activation reactions of aromatic compounds (see scheme; BAr(f)(4)(-) =tetrakis[(3,5-trifluoromethyl)phenyl]borate; F yellow, Pt red). NHC substituents that are not highly branched prevent agostic interactions and reduce the barriers to achieve the C-H bond cleavage.     

Intermolecular C-H bond activation promoted by a titanium alkylidyne

The transient titanium alkylidyne complex (PNP)TiCtBu (PNP = N-[2-P(CHMe2)2-4-methylphenyl]2-), prepared from alpha-hydrogen abstraction of the corresponding alkylidene-alkyl species (PNP)Ti=CHtBu(CH2tBu), can readily undergo intermolecular 1,2-addition of C-H bonds of benzene and SiMe4. Synthesis and reactivity, isotopic labeling, kinetics, and theoretical studies strongly favor an alkylidyne pathway and the alpha-H abstraction step to be the rate-determining step.     

Intermolecular coupling of alkenes to heterocycles via C-H bond activation

The intermolecular coupling of unactivated alkenes to a range of heterocycles using a Rh(I) catalyst was investigated. A variety of functional groups were incorporated into the alkene, including esters, nitriles, acetals, and phthalimide. Furthermore, the heterocycle tolerated substitution with both electron-rich and electron-deficient groups. The intermolecular coupling became possible after it was discovered that weak acids dramatically increase the rate of both the inter- and intramolecular reactions. An extensive optimization of additives was performed, and HCl.PCy(3) (Cy = cyclohexyl) and HCl.P-t-Bu(2)Et were in general found to be the best additives for the reaction.     

Iron-catalyzed direct arylation through directed C-H bond activation

An iron-catalyzed C-C bond formation reaction of a nitrogen-containing aromatic compound with an arylzinc reagent takes place at 0 degrees C in a good to quantitative yield. The reaction involves a C-H bond activation directed by a neighboring nitrogen atom. The important additives in this reaction are 1,10-phenanthroline, tetramethylethylenediamine, and 1,2-dichloro-2-methylpropane, in the absence of which a very low product yield was observed.     

Synthesis of a beta-diiminate iridium tetrahydride for arene C-H bond activation

The preparation of the iridium tetrahydride ((iPr)BDI)IrH(4)[BDI = ArNC(Me)CH(Me)CNAr, Ar = 2,6-(i)Pr(2)C(6)H(3)] and its activity in the catalytic C-H activation of arenes is described.     

Enantioselective synthesis of a PKC inhibitor via catalytic C-H bond activation

[reaction: see text] The syntheses of two biologically active molecules possessing dihydropyrroloindole cores (1 and 2) were completed using rhodium-catalyzed imine-directed C-H bond functionalization, with the second of these molecules containing a stereocenter that can be set with 90% ee during cyclization using chiral nonracemic phosphoramidite ligands. Catalytic decarbonylation and direct indole/maleimide coupling provide efficient access to 2.     

Direct sp3 C-H bond activation adjacent to nitrogen in heterocycles

Activation of sp(3) C-H bonds adjacent to nitrogen in heterocycles is an attractive transformation that is emerging as a practical method in organic synthesis. This tutorial review aims to summarize the key examples of direct functionalization of nitrogen-containing heterocycles via metal-mediated and metal-catalyzed processes, which is meant to serve as a foundation for future investigations into this rapidly developing area of research. The review covers functionalization of N-heterocycles via alpha-lithiation with alkyllithium/diamine complexes, alpha-amino radical formation, metal-catalyzed direct C-H activation, C-H oxidations and oxidative couplings, and metal-catalyzed carbene insertions.     

基于铁催化的C-H键活化构建C-C键的研究进展

过渡金属催化的C-H键活化及在此基础上的C-C键形成的反应因其高原子经济性和高效的合成效率而备受人们的关注.铁元素具有含量丰富、廉价、易得、环境友好等优点,在催化反应中得到了越来越广泛的应用.近几年来,人们关于Fe催化的C-H键活化构建C-C键反应的研究也取得了一定的进展.本文对铁催化的C-H键活化构建C-C键的最新研究进展作了综述,并且按照铁催化剂的不同价态进行了分类归纳,也对催化机理进行了阐述与总结.     

Synthesis of a tricyclic mescaline analogue by catalytic C-H bond activation

[reaction: see text] A tetrahydrobis(benzofuran) mescaline analogue has been prepared in six steps and 38% overall yield from (4'-O-methyl)methyl gallate. The key step in this synthesis is a tandem cyclization reaction via directed C[bond]H activation followed by olefin insertion.     

Intramolecular C-H bond activation induced by a scandium terminal imido complex

A CpPN-based scandium terminal imido complex was isolated, which could induce the intramolecular C-H bond activation of a phenyl group even at room temperature.     

Microwave-assisted C-H bond activation: a rapid entry into functionalized heterocycles

[reaction: see text] Microwave irradiation strongly accelerates the rhodium-catalyzed intramolecular coupling of a benzimidazole C-H bond to pendant alkenes. The cyclic products were formed in moderate to excellent yields with reaction times less than 20 min. Additionally, the use of microwave irradiation allowed the reactions to be performed without any solvent purification and with minimal precautions to exclude air.